Gas generator

ABSTRACT

A gas generator, especially for a vehicle safety system, has a pyrotechnical igniter unit ( 22 ) and a holder ( 14 ) for the igniter unit ( 22 ). The igniter unit ( 22 ) is attached to the holder ( 14 ) in that the igniter unit ( 22 ) and the holder ( 14 ) are encapsulated together by one of injection molding and foaming of a plastic. The holder ( 14 ) has at least one passage opening ( 30, 38 ) for the plastic during the encapsulation by one of injection molding and foaming, the at least one opening being configured in such a way as to create a form-fitting anti-twist protection between the plastic ( 34 ) and the holder ( 14 ).

TECHNICAL FIELD

The present invention relates to a gas generator, especially for avehicle safety system, having a pyrotechnical igniter unit and a holderfor the igniter unit, the igniter unit being attached to the holder inthat the igniter unit and the holder are encapsulated together byinjection molding or foaming.

BACKGROUND OF THE INVENTION

Gas generators are used especially for vehicle occupant restraintsystems in the form of airbags or belt tensioners. Various types of gasgenerators exist, namely, purely pyrotechnical generators, compressedgas generators in which the pressurized gas is released by the igniterunit, or else hybrid gas generators. The igniter unit is a hermeticallysealed, prefabricated unit and it has to be directly or indirectlycoupled to the outer housing of the gas generator in a fixed position.Normally, a section of the outer housing is used as the holder, that isto say, the part to which the igniter unit is directly attached. Ignitercontacts and also the plastic used for the encapsulation by injectionmolding and/or foaming protrude through a passage opening in the holder,as a result of which sections of the igniter unit and, at the same time,the holder are embedded in the plastic. The plastic is intended toattach the igniter unit to the holder and also to seal the passageopening so that it is gas-tight as well as moisture-tight.

The object of the invention is to make a gas generator of theabove-mentioned type even more gas-tight in the area of the transitionfrom the holder to the igniter unit.

BRIEF SUMMARY OF THE INVENTION

This is achieved in a gas generator, especially for a vehicle safetysystem, having a pyrotechnical igniter unit and a holder for the igniterunit. The igniter unit is attached to the holder in that the igniterunit and the holder are encapsulated together by one of injectionmolding and foaming of a plastic. The holder has at least one passageopening for the plastic during the encapsulation by one of injectionmolding and foaming, the at least one opening being configured in such away as to create a form-fitting anti-twist protection between theplastic and the holder. For gas generators employed so far, a centered,circular passage opening was provided in the holder, which has thedrawback that the plastic and the holder only established an adhesiveconnection in the twisting direction, that is to say, around the axis ofthe opening. Therefore, this connection has to be handled relativelycarefully so that it does not become detached, allowing moisture topenetrate into the gas generator. In contrast, with the invention, inaddition to the adhesive connection in the twisting direction, aform-fitting connection is also created between the plastic and theholder, this form-fitting connection preventing such a detachment. Theform-fitting connection between the plastic and the igniter unit in thetwisting direction is normally established in that several ignitercontacts on the back of the igniter unit protrude into the plastic.

According to a preferred embodiment, the passage opening isout-of-round.

Another possible configuration for the passage opening is that it isprovided with a notch protruding laterally outwards relative to thepassage opening, the notch acting as an anti-twist protection.

As an alternative, of course, several passage openings can be provided.

As already mentioned above, the holder is especially a section of anouter housing of the gas generator.

The igniter contacts preferably protrude through the holder andespecially are part of the igniter unit and form a prefabricated unittogether with said igniter unit.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a cross section through an embodiment of the gas generatoraccording to the invention,

FIG. 2 shows a top view of the holder used in the embodiment of FIG. 1and

FIG. 3 shows a top view of an alternative holder that can be used inFIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows a pyrotechnical gas generator that has a two-shell outerhousing 10 being constituted of a pot-shaped upper part 12 and apot-shaped lower part 14. The pot-shaped lower part 14 has anindentation 16 shaped by deep-drawing that serves to accommodate anigniter connector (not shown here). A combustion chamber 20 filled withpyrotechnical propellant 18 is provided inside the gas generator 10. Inorder to ignite the propellant 18, a prefabricated igniter unit 22 isused, which is situated in the center of the combustion chamber 20 andwhich has a cylindrical head 23 filled with pyrotechnical means as wellas igniter contacts 24 that form part of the igniter unit and thatprotrude from a backside of said igniter unit. A lid-shaped housing 26surrounding the head 23 of the igniter unit 22 receives a booster charge28.

The lower part 14 of the housing 10 is shown in FIG. 2 in a slightlyenlarged depiction. It is a deep-drawn metal part that has a centeredpassage opening 30 through which the two igniter contacts 24 canprotrude. The passage opening 30 is out-of-round since it has fourlateral notches 32 protruding outwards. Although a circular bore wasmade in the center of the passage opening, the passage opening becomesout-of-round because of the notches 32. Of course, it is also possibleto have a passage opening 30 that is oval, angular or delimited by flatsides.

The igniter unit 22 is connected to the holder 14 through encapsulationby injection molding or foaming in that these two parts are placed intoan injection molding or foaming tool. The inserted liquid plastic 34penetrates into and fills up an annular interstice between thetool—which simulates what will later be the housing 26—and the head 23.The plastic also fills up the interstice in the vertical direction fromthe head 23 to the plateau-like elevation of the holder 14, as well asthe entire passage opening 30 along with the notches 32 and finally alsothe lower indentation 16 in the holder 14, except for a receptacle forthe igniter connector that will later be connected to the ignitercontacts 24.

As a result, the igniter unit 22 and the holder 14 are embedded in theplastic 34 so that the igniter unit 22 is connected to the holder 14 ina fixed position.

Subsequently, the booster charge 28 is filled into the lid 26 and theunit created by injection molding and/or foaming is inserted into thelid 26.

Consequently, in the area of the out-of-round passage opening 30 that isprovided with the notches 32 and that is completely filled with plastic34, a mechanical anti-twist protection is created between the curedplastic 34 and the holder 14, this anti-twist protection preventing theplastic 34 from being loosened or detached from the holder 14 whenexcessive force is exerted from the outside.

In the embodiment according to FIG. 3, in addition to the circularcentral passage opening 30, four additional passage openings 38 areprovided that are likewise filled with plastic 34 so that these passageopenings 38 with their smaller cross section create the anti-twistprotection.

1. A gas generator, especially for a vehicle safety system, having apyrotechnical igniter unit (22) and a holder (14) for said igniter unit(22), said igniter unit (22) being attached to said holder (14) in thatsaid igniter unit (22) and said holder (14) are encapsulated together byone of injection molding and foaming of a plastic, said holder (14)having at least one passage opening (30, 38) for said plastic duringsaid encapsulation by one of injection molding and foaming, said atleast one opening being configured in such a way as to create aform-fitting anti-twist protection between said plastic (34) and saidholder (14).
 2. The gas generator according to claim 1, wherein saidpassage opening (30) is out-of-round.
 3. The gas generator according toclaim 1, wherein said passage opening (30) has a notch (32) protrudinglaterally outwards.
 4. The gas generator according to claim 1, whereinseveral passage openings (30, 38) are provided.
 5. The gas generatoraccording to claim 1, wherein a central passage opening (30) isprovided.
 6. The gas generator according to claim 1, wherein said holder(14) is a section of an outer housing (10) of said gas generator.
 7. Thegas generator according to claim 1, wherein igniter contacts (24) ofsaid igniter unit (22) protrude through said holder (14).
 8. The gasgenerator according to claim 7, wherein said igniter contacts (24) arepart of said igniter unit (22) and form a prefabricated unit togetherwith said igniter unit (22).